Hi Keith
your friend sounds like he's been boxing for awhile, so its no surprise with the difference in experience. As mentioned above, don't bring a punching match to a boxer.

The subtleties of Aikido can be modified to be quite destructive. eg. direct Iriminage or arm break from shihonage. At the moment, you are learning where to put your hands and where to put your feet. In the dojo we accomodate each other to learn the correct movement.
I understand that you would like to try out the techniques but for now you have to learn the basics.

don't get me wrong, I am not condoning (not sure if this word is in the right context?) sparring Aikido vs MMA or boxing etc. I always believe its the martial artist and not the martial arts thats a factor. If if you want a quick martial art for grapelling or combat, then maybe you should look for another martial art

don't have to feel helpless/defenseless with him... he's your friend right? just look at it as part of training.